1. Field of the Invention
The present invention relates to a process for toughening a surface of a support for a lithographic printing plate, and particularly relates to such a surface roughening process which is performed by electrochemical processing, which is superior in print performance, and which is simple and easy.
2. Description of the Related Art
In an electrochemical surface treating process for a support for a lithographic printing plate, it is important to improve a printing durability, a scumming resistance, and a fill-in reduction by controlling the grained surface structure.
U.S. Pat. No. 5,304,298 proposes a process for roughening aluminum or aluminum alloys useful as support material for printing plates, in which the process having two electrochemically roughening steps are carried out in direct succession and are followed by a pickling step. Printing plates are produced from this support material by coating with light-sensitive coatings, which printing plates, when exposed and developed, give corresponding printing formes of very uniform topography, high run stability and good damping agent supply.
The process can be carried out discontinuously or continuously with strips of aluminum or its alloys in the U.S. Pat. No. 5,304,298. This patent discloses preferable process parameters in the continuous process during the roughening steps, for example, the temperature of electrolyte, the current density, the dwell time in the electrolyte of a section of material to be roughened, and the electrolyte flow rate at the surface of the material to be roughened. FIG. 1 is a side view of a conventional example having no pause section.
In the above conventional process, however, the ranges are defined strictly with respect to all the conditions and it is difficult to obtain optimum conditions.